netdev - [PATCH] drivers/net/b44: Change to non-atomic bit operations

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Date:   Fri, 20 Dec 2019 15:29:11 -0800
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     "Michael Chan" <michael.chan@...adcom.com>, netdev@...r.kernel.org
Cc:     "Thomas Gleixner" <tglx@...utronix.de>,
        "Andy Lutomirski" <luto@...nel.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Tony Luck" <tony.luck@...el.com>,
        "David Laight" <David.Laight@...LAB.COM>,
        "Ravi V Shankar" <ravi.v.shankar@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>
Subject: [PATCH] drivers/net/b44: Change to non-atomic bit operations

Since "pwol_mask" is local and never exposed to concurrency, there is
no need to set bit in pwol_mask by costly atomic operations. On x86,
accessing data across two cache lines in one atomic bit operation
(aka split lock) can take over 1000 cycles.

Directly operate on the byte which contains the bit instead of using
__set_bit() to avoid any big endian concern due to type cast to
unsigned long in __set_bit().

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
---
 drivers/net/ethernet/broadcom/b44.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/b44.c b/drivers/net/ethernet/broadcom/b44.c
index 035dbb1b2c98..ec25fd81985d 100644
--- a/drivers/net/ethernet/broadcom/b44.c
+++ b/drivers/net/ethernet/broadcom/b44.c
@@ -1516,8 +1516,10 @@ static int b44_magic_pattern(u8 *macaddr, u8 *ppattern, u8 *pmask, int offset)
 	int ethaddr_bytes = ETH_ALEN;
 
 	memset(ppattern + offset, 0xff, magicsync);
-	for (j = 0; j < magicsync; j++)
-		set_bit(len++, (unsigned long *) pmask);
+	for (j = 0; j < magicsync; j++) {
+		pmask[len >> 3] |= BIT(len & 7);
+		len++;
+	}
 
 	for (j = 0; j < B44_MAX_PATTERNS; j++) {
 		if ((B44_PATTERN_SIZE - len) >= ETH_ALEN)
@@ -1529,7 +1531,8 @@ static int b44_magic_pattern(u8 *macaddr, u8 *ppattern, u8 *pmask, int offset)
 		for (k = 0; k< ethaddr_bytes; k++) {
 			ppattern[offset + magicsync +
 				(j * ETH_ALEN) + k] = macaddr[k];
-			set_bit(len++, (unsigned long *) pmask);
+			pmask[len >> 3] |= BIT(len & 7);
+			len++;
 		}
 	}
 	return len - 1;
-- 
2.19.1